Zeolite composite film and process for producing the same

ABSTRACT

A method for producing a zeolite composite membrane in which a zeolite membrane is formed on a porous substrate includes the steps of: coating a zeolite membrane on a porous substrate made of zeolite having the same or a similar composition as the zeolite membrane and containing the same template as the zeolite membrane; and calcining the porous substrate having the zeolite membrane thereon to remove the template from the zeolite membrane and the porous substrate at once. A zeolite composite membrane that does not have cracks can be obtained by almost equalizing thermal expansion coefficients of the porous substrate and the zeolite membrane.

TECHNICAL FIELD

The present Invention relates to a zeolite composite membrane and amethod for producing the zeolite composite membrane, and morespecifically, a zeolite composite membrane having a zeolite membranewithout cracks formed on a substrate and a method for producing thezeolite composite membrane.

BACKGROUND ART

There has been hitherto known a zeolite composite membrane having azeolite membrane formed on a surface of a substrate. In addition,various methods for producing such a zeolite composite membrane havebeen proposed.

Japanese Patent Laid-Open 59-213615 discloses a substrate for a zeolitemembrane in which a substrate of metal or the like is covered withceramics of glass, mullite, and cordierite type, or alumina, silica, orminerals.

Japanese Patent Laid-Open 60-28826 discloses a composite membrane inwhich a thin membrane made of cage-shaped zeolite is united with aporous support of an inorganic or a high molecular substance on itssurface. Good results have been obtained by the use of a support havinghigh compatibility with a gel substance. For example, it is mentionedthat a material No. 7930 from Corning Glass Works Co., Ltd., or onegenerally refired to as Vycor glass is particularly preferable as asupport.

Japanese Patent Laid-Open 1-148771 relates to a method for crystallizingzeolite on a surface of a monolithic ceramic support and discloses amonolithic support having an oxide composition containing 45-4 wt % ofsilica, 8-45 wt % of alumina, and 7-20 wt % of magnesia, specifically, asintered monolithic support made of cordierite, glass, or glass ceramic.

Japanese Patent Laid-Open 6-32610 relates to a method for producing anA-type or a faujasite-type zeolite membrane and discloses a substratemade of a substance containing silicon oxide as a main component. Themethod aims to improve bad adhesion to a substrate. A substrate itselfis made of a material of a zeolite membrane in the method, and a surfaceof the substrate is covered with a zeolite membrane. Therefore,synthesis and impregnation can simultaneously proceed, and processes aresimplified. Examples of a material of the substrate are borosilicateglass, quartz glass, silica alumina, and mullite.

Japanese Patent Laid-Open 9-173799 relates to a method for forming aloaded zeolite membrane and the membrane and discloses a substrate madeof a ceramic substance basically containing alumina, zirconia, ortitanium oxide; an inorganic, an organic, or a mixed substance selectedfrom the group consisting of metal, carbon, silica, zeolite, clay andpolymer.

Thus, zeolite composite membranes having a zeolite membrane on a surfaceof a substrate has conventionally been known. However, it has been foundthat these composite membranes have the following problem:

That is, as shown in FIG. 3, zeolite shows very complex characteristicsin that zeolite has a very small thermal expansion coefficient at atemperature up to about 200° C. and a negative coefficient at a highertemperature. Therefore, when a zeolite membrane is used at a temperatureover 200° C., difference in thermal expansion coefficient between thezeolite membrane and a substrate, for example, an alumina substrateextremely increases, thereby causing a crack in the zeolite membrane bya thermal stress.

Depending on kind of a zeolite membrane, it is required to add atemplate or a crystal directing agent upon synthesis. A zeolite membranecontaining a template is subjected to calcination at about 500° C. toremove the template. Since thermal expansion behavior of a zeolitemembrane containing a template is remarkably different from that of azeolite membrane containing no template (thermal expansion curve in FIG.3 and thermal expansion curve in FIG. 4), a difference in thermalexpansion between a zeolite membrane containing a template and asubstrate, for example, an alumina substrate is extremely large, therebycausing a crack in the zeolite membrane due to thermal stress duringcalcination.

The present invention has been made in view of the conventional problemsand alms to provide a zeolite composite membrane without any cracks byusing a substrate having the same or a similar composition as a zeolitemembrane upon forming a zeolite membrane on a surface of the substrateto almost equalize thermal expansion coefficients of the substrate andthe zeolite membrane and a method for producing the zeolite compositemembrane.

SUMMARY OF INVENTION

According to the present invention, there is provided a zeolitecomposite membrane comprising:

a zeolite membrane, and

a porous substrate made of a zeolite having the same or a similarcomposition as said zeolite membrane;

wherein said zeolite membrane is formed on said porous substrate.

According to the present invention, there is further provided a zeolitecomposite membrane intermediate comprising:

a zeolite membrane containing a template, and

a porous substrate made of zeolite having the same or a similarcomposition as said zeolite membrane and containing the same template assaid zeolite membrane;

wherein said zeolite membrane is formed on said porous substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a photograph showing a structure of particles in a crosssection of a zeolite compound membrane obtained in Example 1.

FIG. 2 is a graph showing a result of X-ray diffraction showing aMFI-type zeolite membrane.

FIG. 3 is a graph showing a thermal expansion curve of MFI-type zeolite.

FIG. 4 is a graph showing a thermal expansion curve of MFI-type zeoliteand alumina.

FIG. 5 is a schematic view shown a method for measuring a crack bypervaporation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has been accomplished on the basis of finding thatthermal expansion behavior of a zeolite membrane containing a templateis extremely different from a zeolite membrane containing no template asshown in FIGS. 3 and 4.

That is, a thermal expansion difference upon calcining at about 500° C.to remove a template cannot be solved only by producing a zeolitecomposite membrane using a substrate having a thermal expansioncoefficient close to that of the zeolite membrane, and a crack is causedin the zeolite membrane. Therefore, in the present invention, there areused a zeolite membrane containing a template and a porous substratemade of zeolite having the same or a similar composition as the zeolitemembrane and containing the same casting agent as the zeolite membrane.

The present invention is hereinbelow described in more detail.

A zeolite composite membrane of the present invention includes a zeolitemembrane and a porous substrate having the same or a similar compositionas the zeolite membrane.

As zeolites showing a non-liner extraordinary behavior of thermalexpansion, there are known MFI, DOH, DDR, MTN, and AFI (refer ParkS. H.Etal. Stud. Surf. Sci. Catal. 1997, 105, 1989-1994).

As a zeolite membrane requiring a template, there are hydroxide orbromide of TPA (tetrapropyl ammonium) for a MFI-type, hydroxide orbromide of TEA (tetraethyl ammonium) for a BEA-type, or the like,Thermal expansion behavior extraordinary differs between a zeolitemembrane containing a template and a zeolite membrane containing notemplate as shown in FIGS. 3 and 4.

Therefore, in the present invention, when a zeolite membrane containinga template is coated on a porous substrate, a porous substratecontaining the same template and made of zeolite having the same or asimilar composition as the zeolite membrane is used. On the other hand,when a zeolite membrane containing no template, a porous substratecontaining no template and made of zeolite having the same or a similarcomposition as the zeolite membrane is used.

As a method for producing the zeolite membrane for coating the poroussubstrate, there may be employed a conventionally known method, forexample, hydrothermal synthesis and vapor-phase transport.

That is any of the following methods may be employed:

(1) A method in which a zeolite powder is formed with a binder;

(2) A method in which a zeolite powder is formed with a binder, and thebinder is transformed into a zeolite by a chemical treatment;

(3) A method in which a zeolite precursor is molded and then transformedinto a zeolite by a heat treatment.

Examples of the above binder-addition method (1) are a method in which asol such as a silica sol is added to zeolite (Japanese Patent Laid-Open2-4445), and a method in which an attapulgite-type clay and carboxylmethyl cellulose are added to zeolite (Japanese Patent Laid-Open10-81511).

Examples of the above binderless method (2) are a method in which kaolinis added to and mixed with zeolite, fired, and subjected to ahydrothermal treatment to transform caolin into zeolite (Japanese PatentLaid-Open 10-101326), and a method in which methakaolin is mixed withzeolite and subjected to an alkali treatment to transform methakaolininto zeolite (Japanese Patent Laid-Open 52-103391).

Examples of the above zeolite solid-phase synthesis method (3) are amethod in which template (a casting agent) is mixed with kanemite toobtain an amorphous silicate powder and subjected the amorphous silicatepowder to molding and a heat treatment to obtain zeolite such as MFI(Patent No. 2725720), and a method in which a mixture of TEOS andtemplate is subjected to hydrolysis and drying to obtain an amorphoussilicate powder, and the powder is subjected to molding and a heattreatment to obtain zeolite (Shimizu, S., Kiyozumi Y. & Mizukami F.Chem. Lett., 1996, 403-404).

Since a crack formed in a zeolite due to a difference in thermalexpansion at a molecular level of about 8-50 Å, it cannot be detectedeven by SEM. Therefore, the following methods are employed in thepresent invention as a method for measuring the aforementioned crack.

As the first method, a crack made visible by dropping Rhodamine B on thezeolite membrane is observed with an optical microscope.

The second method is a pervaporation, wherein the triisopropyl benzene(TIPB) molecule 10 is sucked by a vacuum pump 12 to make the molecule 10pass the zeolite membrane 11, as shown in FIG. 5, to confirm presenceand absence of a crack by a vacuum gauge 13 or a gas chromatograph.

The present invention is concretely described with reference toexamples. However, the present invention is by no means limited to theseexamples.

EXAMPLE 1

20.00 g of about 30 wt % of silica sol (Snowtex S produced by NissanChemical, Industries, Ltd.) and 20.34 g of tetrapropyl ammoniumhydroxide solution (produced by Wako Pure Chemical Industries, Ltd.) wasstirred in a 200 ml Teflon beaker by a magnetic stirrer for 30 minutesat room temperature to obtain a mixture. The mixture was heated at 80°C., and the stirring was continued until water is evaporated and anevaporated water no longer condenses to the surface of a wall to obtaincolorless dried gel. On investigation, a crystal structure of theobtained dried gel was noncrystalline.

This dried gel was ground by an agate mortar, and powder particlespassed through a 355 μm-mesh screen was subjected to one-axis press toobtain a molded body having a thickness of 2-3 mm. The molded body wasdisposed on filter paper in a stainless 100 ml pressure container havinga Teflon inner cylinder containing 0.3 ml of distilled water so that themolded body does not contact water and reacted under spontaneous vaporpressure for 16 hours in an oven at a temperature of 130° C. Then, themolded body was subjected to X-ray diffraction, its component was MFIzeolite. The molded body was sufficiently dried at 80° C. to obtain azeolite substrate.

20.34 g of 10% tetrapropyl ammonium hydroxide solution (produced by WakoPure Chemical Industries, Ltd.) was mixed with 2.00 g of tetrapropylammonium bromide (produced by Wako Pure Chemical Industries, Ltd.) toobtain a mixture. Further, 49.85 g of distilled water, 6.00 g of about30wt % of silica sol (Snowtex S produced by Nissan Chemical Industries,Ltd.) was added to the mixture, and the mixture was stirred with amagnetic stirrer for 30 minutes at room temperature to obtain sol forforming a membrane.

This sol was put in a pressure stainless 100 ml pressure containerhaving a Teflon inner cylinder, the zeolite substrate was immersed inthe sol, and the sol was subjected to a reaction for 18 hours in an ovenat 180° C. A cross-section after the completion of the reaction wasobserved by scanning electron microscope (SEM), and it was found that aminute layer having a thickness of about 17 μm was formed on the porouszeolite substrate as shown in a scanning electron microscope (SEM)photograph of FIG. 1 and that this minute layer was a MFI-type zeolitemembrane from X-ray diffraction as shown in FIG. 2.

A zeolite composite membrane intermediate obtained above was heated upto 500° C. in an electric furnace, and it was kept for 4 hours to removetetrapropyl ammonium. As shown in FIG. 1, no crack was observed in thezeolite composite by Rhodamine test. In addition, no molecule passed bya pervaporation of triethylbenzene, and it was found that the zeolitecomposite membrane was minute with no crack.

EXAMPLE 2

A dry gel molded body was disposed on filter paper in a stainless 100 mlpressure container having a Teflon inner cylinder containing 0.3 ml ofdistilled water so that the molded body does not contact water andreacted under spontaneous vapor pressure for 4 hours in an oven at atemperature of 130° C. Then, the molded body was subjected to X-raydiffraction, its component was MFI zeolite. The molded body wassufficiently dried at 80° C. to obtain a zeolite substrate.

The substrate was immersed in the same sol as in Example 1 and put in astainless 100 ml pressure container having a Teflon inner cylinderreacted for 18 hours in an oven at 180° C. A cross-section after thecompletion of the reaction was observed by SEM, and it was found thatthe same minute layer as shown in Example 1 was formed on the porouszeolite substrate and that this minute layer was a MFI-type zeolitemembrane from X-ray diffraction. Further, a portion of the substrate,which was noncrystalline before the membrane was formed, was convertedinto a MFI-type zeolite by a membrane-forming treatment. Thus, a zeolitecomposite membrane intermediate having a zeolite membrane formed on azeolite porous substrate was obtained.

A zeolite composite membrane intermediate obtained above was heated upto 500° C. in an electric furnace, and it was kept for 4 hours to removetetrapropyl ammonium. As shown in FIG. 1, no crack was observed in thezeolite composite by Rhodamine test. In addition, no molecule passed bya pervaporation of triethylbenzene, and it was found that the zeolitecomposite membrane was minute with no crack.

COMPARATIVE EXAMPLE 1

A zeolite membrane was formed in the same manner by immersing a porousalumina in a sol prepared in the same manner as in Example 1.

This membrane was heated up to 500° C. in an electric furnace, and itwas kept for 4 hours to remove tetrapropyl ammonium. As shown in FIG. 1,a crack was observed in the zeolite composite by Rhodamine test. Inaddition, molecules passed by a pervaporation of triethylbenzene, and itwas found that the zeolite composite membrane was not minute.

COMPARATIVE EXAMPLE 2

A zeolite membrane was formed in the same manner by immersing a poroussilicon nitride in a sol prepared in the same manner as in Example 1.

This membrane was heated up to 500° C. in an electric furnace, and itwas kept for 4 hours to remove tetrapropyl ammonium. As shown in FIG. 1,a crack was observed in the zeolite composite by Rhodamine test. Inaddition, molecules passed by a pervaporation of triethylbenzene, and itwas found that the zeolite composite membrane was not minute.

COMPARATIVE EXAMPLE 3

A zeolite membrane was formed in the same manner by immersing a porousmullite in a sol prepared in the same manner as in Example 1.

This membrane was heated up to 500° C. in an electric furnace, and itwas kept for 4 hours to remove tetrapropyl ammonium. As shown in FIG. 1,a crack was observed in the zeolite composite by Rhodamine test. Inaddition, molecules passed by a pervaporation of triethylbenzene, and itwas found that the zeolite composite membrane was not minute.

COMPARATIVE EXAMPLE 4

A zeolite membrane was formed in the same manner by immersing a poroussilica glass in a sol prepared in the same manner as in Example 1.

This membrane was heated up to 500° C. in an electric furnace, and itwas kept for 4 hours to remove tetrapropyl ammonium. As shown in FIG. 1,a crack was observed in the zeolite composite by Rhodamine test. Inaddition, molecules passed by a pervaporation of triethylbenzene, and itwas found that the zeolite composite membrane was not minute.

COMPARATIVE EXAMPLE 5

A zeolite membrane was formed in the same manner by immersing a porouscordierite in a sol prepared in the same manner as in Example 1.

This membrane was heated up to 500° C. in an electric furnace, and itwas kept for 4 hours to remove tetrapropyl ammonium. As shown in FIG. 1,a crack was observed in the zeolite composite by Rhodamine test. Inaddition, molecules passed by a pervaporation of triethylbenzene, and itwas found that the zeolite composite membrane was not minute.

TABLE 1 Crack TIPB molecule Example 1 None Blocked Example 2 NoneBlocked Comparative Example 1 Present Passed Comparative Example 2Present Passed Comparative Example 3 Present Passed Comparative Example4 Present Passed Comparative Example 5 Present Passed

Industrial Applicability

As described above, according to the present invention, there isprovided a zeolite composite membrane without any crack by using asubstrate having the same or a similar composition as a zeolite membraneupon forming a zeolite membrane on a surface of the substrate to almostequalize thermal expansion coefficients of the substrate and the zeolitemembrane.

Such a zeolite composite membrane can suitably be used as a separationmembrane for separating substance, an adsorbent, a catalyst in thepetrochemical industry, etc.

What is claimed is:
 1. A zeolite composite membrane comprising: azeolite membrane having a crystal structure, and a porous substrate madeof a zeolite having the same crystal structure as said zeolite membrane;wherein said zeolite membrane is formed directly on said poroussubstrate, and said porous substrate is self-supporting.
 2. A zeolitecomposite membrane according to claim 1, wherein said zeolite is oneselected from the group consisting of MFI, AFI, DDR, DOH, MTN and BEA.3. A zeolite composite membrane intermediate comprising: a zeolitemembrane having a crystal structure and containing a template, and aporous substrate made of zeolite having the same crystal structure andcontaining the same template as said zeolite membrane; wherein saidzeolite membrane is formed directly on said porous substrate, and saidporous substrate is self-supporting.
 4. A zeolite composite membraneintermediate according to claim 3, wherein said zeolite is one selectedfrom the group consisting of MFI, AFI, DDR, DOH, MTN and BEA.
 5. Amethod for producing a zeolite composite membrane in which a zeolitemembrane is formed on a porous substrate, comprising the steps of:coating a zeolite membrane on a porous substrate made of a zeolitehaving the same crystal structure as said zeolite membrane, said zeolitemembrane including a template and said porous substrate containing thesame template as said zeolite membrane; and calcining the poroussubstrate having the zeolite membrane thereon to remove the templatefrom the zeolite membrane and the porous substrate at once, wherein saidzeolite membrane is formed directly on said porous substrate, and saidporous substrate is self-supporting.
 6. A method for producing a zeolitecomposite membrane according to claim 5, wherein said zeolite is oneselected from the group consisting of MFI, AFI, DDR, DOH, MTN and BEA.